Conventional dynamic communication switches provide system-wide, non-blocking connectivity. The structure and operation of such switches are well known, having been described in many publically available documents such as U.S. Pat. No. 4,635,250 to Georgiou and U.S. Pat. No. 4,630,045 to Georgiou.
These conventional switches each include a centralized system clock that is used to synchronize data transfers from port to port through a matrix switch. At high bit-rates, however, the design of the centralized system clock to assure proper data synchronization becomes very complex.
A possible solution for relieving the demands on the centralized system clock and data synchronization is to transfer the data between the ports and the switching matrix in parallel form. However, as data rates and size of the switching matrix increase, parallel data transfer becomes a very difficult implementation problem due to the large number of signal lines needed. Specifically, it becomes difficult to simultaneously clock all the signal lines. This problem is called clock skewing.
In addition to synchronously transferring data between the ports and matrix switch, the conventional switches ordinarily transfer control information between the ports and matrix switch in a synchronous fashion. Consequently, the design of the centralized system clock is further complicated since clocks of different rates are required.
A prior solution to the above problems is presented in U.S. Pat. No. 4,809,260 to Davidson et al. Davidson describes a telephone time division multiplex (TDM) non-blocking switching system arranged in a star topology. The transmission of data through the switching system is done utilizing a self-clocking pulse code modulation (PCM) technique (Manchester code). The data is extracted at each destination by using a clock-bit incorporated in every data bit cell. This prior solution is flawed, however, as it reduces the effective bandwidth of the links by 50%.